Solid-state laser

ABSTRACT

In order to improve a solid-state laser comprising a resonator, at least one solid-state rod arranged in the resonator and a pumping power source for exciting the solid-state rod such that the dissipation heat can be controlled better and excitation for high powers is possible in a simple way, it is proposed that the resonator be a coupled resonator, that the resonator have two elongated excitation sections lying in one plane with one of the solid-state rods being arranged in their respective beam, that the resonator have a coupling section which the beams of the excitation sections enter as outer beams extending parallel to one another but in spaced relation to one another and which couples the excitation sections with one another by displacement of the outer beams in the plane defined by these to a coupling axis lying parallel to and between the outer beams and beyond this coupling axis, and that irradiated by the pumping power source on another side surface.

The invention relates to a solid-state laser comprising a resonator, atleast one laser amplification volume arranged in the resonator and apump means for exciting the laser amplification volume.

In all hitherto known solid-state lasers such as optically pumpedsolid-state rod lasers or semiconductor lasers, problems arise with thecontrolling of the dissipation heat.

when unfiltered light from gas-discharge lamps is used as pumping powersource, one has to assume that, for example, in the case of the Nd laserapproximately three times the obtainable laser power will remain as heatin the solid-state rod. This heat causes temperature gradients which inindividual cases result in breakage of the crystals, but at any rate inoptical deformations. For these reasons, today's solid-state lasers aresubject to a power limit which does not permit multi-kilowatt operationif the beam quality is still to be good and adaptable to changingoperating conditions.

A further problem of the known optically excited solid-state lasersresides in the design of the excitation light source. With a total laserefficiency of a few percent, the excitation lamps have to convert up to100 kW if the laser is to generate a few kW laser power. This powerconcentration can only take place in larger volumes and surfaces. On theother hand, the emitted light has to be directed at the active medium.The latter should absorb the excitation light as completely as possible,which requires a layer thickness of several mm.

The same problems occur with the semiconductor laser where, in addition,a laser-active semiconductor layer region cannot be of optional,large-volume configuration if purposeful laser amplification is to beachieved.

In view of these disadvantages of the prior art, the object underlyingthe invention is to so improve a solid-state laser of the generic kindthat it is suitable for generating high power.

This object is accomplished in accordance with the invention in asolid-state laser comprising a laser-active unit with a laseramplification volume extending in a first direction in a solid, a pumpmeans associated with the laser amplification volume for exciting it anda resonator with an excitation section which is arranged between itsresonator mirrors and in which a beam extends in a direction ofpropagation and thereby penetrates in the laser amplification volume inthe first direction, by at least two excitation sections being provided,each having one laser amplification volume, by the beams of theexcitation sections extending in spaced relation to one another, by theresonator having a coupling section containing a coherent joint beam ofthe resonator, the cross-section thereof being comprised of severalpartial beams, and by an optical element being arranged between thecoupling section and each excitation section for imaging one of thepartial beams of the joint beam into one of the beams extending inspaced relation to one another in the excitation sections.

The advantage of the inventive solution is that with this solution it ismade possible for the beams of the individual excitation sections to beimaged into partial beams which, for their part, add up in cross-sectionand thereby produce a joint beam in which there is coherent radiationover all of the partial beams. In this way, the amplification of atleast two laser amplification volumes can be used to generate a jointbeam which as such is coherent and has high laser power.

With the invention solution, it is not absolutely necessary for all ofthe partial beams of the joint beam to be imaged into a beam of one ofthe excitation sections. It is also adequate for only individual ones ofthe partial beams of the joint beam to be imaged into a beam of one ofthe excitation sections while the other partial beams of the joint beamdo not experience such imaging. In any case, it is, however, necessaryfor all of the partial beams to be coherent among one another in thejoint beam.

In accordance with the invention, it is particularly advantageous forthe partial beams to form a joint beam which is coherent in thecross-sectional direction.

The optical element can be designed in a variety of different ways and,in particular, the design of the optical element will depend on theshape of the partial beam and of the beam. It is particularlyadvantageous for the optical element to image the respective partialbeam into the beam such that the latter is narrowed in a cross-sectionaldirection with respect to the partial beam. This enables the laseramplification volume to also be made narrower in conformance with thedimensions of the beam in this direction.

In the above description of the inventive solution, the dimensions ofthe laser-active unit were not specified. However, particularlyadvantageous designs of the inventive solid-state layer are obtainableby the laser-active unit having in the cross-sectional direction a widthwhich corresponds at the most to a width of the partial beam imaged bythe optical element onto the beam in this direction. In this way it ismade possible for a partial beam to be imaged into an excitation sectionwithout disturbing the course of the partial beam lying alongside it.

This is, for example, made possible by a partial beam being imaged intothe beam of an excitation section and the partial beam lying alongsideit being allowed to run on alongside the excitation section. Anembodiment of the inventive solution has proven particularlyadvantageous wherein the optical elements of excitation sections lyingalongside one another adjoin one another and image partial beamsimmediately adjacent one another essentially continuously into the beamslying alongside one another and in spaced relation to one another.

In such embodiments wherein the beam is narrowed in the onecross-sectional direction with respect to the partial beam, provision ispreferably made for the laser-active unit to comprise in thiscross-section direction supply elements arranged alongside the laseramplification volume for the latter.

One embodiment of the inventive solution is designed such that the jointbeam is imaged by the optical elements continuously into the beams ofthe excitation sections.

So far no details of the design of the optical elements have been given.The optical elements are preferably designed so as to comprise acylindrical optical means, particularly when the optical elements imagethe partial beam into a beam which is narrowed in a cross-sectionaldirection.

The optical elements can be designed as reflectors or as lenses. Theoptical elements are preferably cylindrical lenses.

Furthermore, it is advantageous for each optical element to imageparallel rays of the joint beam into quasi-parallel rays of the beam sothat, in particular, a joint beam with a substantially parallel path ofrays is imaged into a beams with a likewise substantially parallel pathof rays.

Since the inventive concept is based on the excitation sections beingarranged in spaced relation to one another, this preferably alsoincorporates the laser amplification volumes being spaced in relation toone another.

In a particularly advantageous geometrical configuration, provision ismade for the laser amplification volumes to be arranged at regularspacings from one another.

The solution is preferably designed such that the beams penetratingdifferent laser amplification volumes extend parallel to one another. Inthis way, in particular, a very compact design of the inventivesolid-state laser is achieved.

Since one must work with as high pumping powers as possible in the laseramplification volume in high-power lasers, cooling of the laseramplification volume is expedient, and this cooling is made as effectiveas possible. For this reason, it is advantageous for each laseramplification volume to be cooled on at least one side extendingparallel to the beam. Herein it is even better for each laseramplification volume to be cooled on opposite sides.

In this case, the supply elements mentioned at the beginning preferablycarry out the cooling of the laser amplification volume.

In particular, with laser amplification volumes arranged alongside oneanother, provision is advantageously made for that side on which coolingof the laser amplification volume takes place to be the side facing theadjacent laser amplification volume. This is advantageous particularlywhen this side of the laser amplification volume has a larger surfacethan the side facing away from the adjacent laser amplification volumeas a more effective and, in particular, also more uniform cooling ispossible with this solution.

Furthermore, in the description of the embodiments so far no detailswere given as to the side from which excitation of the laseramplification volume is to take place. It is particularly advantageousfor each laser amplification volume to be excitable from at least oneexcitation side extending parallel to the beam.

Even more optimum excitation is obtained when each laser amplificationvolume is excitable from two opposite excitation sides.

The excitation side can be selected so as to be that side facing awayfrom the adjacent laser amplification volume but, in particular, in asemiconductor laser it is advantageous for the excitation side to be theside facing the adjacent laser amplification volume.

In all of the embodiments described hereinafter, provision is made forat least one laser-active region penetrated by the respective beam to beprovided in each laser amplification volume.

Furthermore, the object mentioned hereinabove is accomplished inaccordance with the invention is a solid-state laser of the kinddescribed at the beginning by the resonator being a coupled resonator,by the resonator having two elongated excitation sections--in particularlying in one plane--with one of the laser amplification volumes beingarranged in their respective beam, by the resonator having a couplingsection which the beam of the excitation sections enter as outer beamsextending in spaced relation to one another --in particular parallel toone another--and which couples the excitation sections with one anotherby displacing the outer beams in the plane defined by these to acoupling axis lying--in particular parallel to the outer beams--betweenthese beyond this coupling axis, and by the laser amplification volumesbeing cooled on side surface extending along the beam and beingexcitable by the pump means from a side surface extending along thebeam.

Hence the inventive solution enables at least two laser amplificationvolumes to be advantageously coupled with one another, with thedissipation heat being controlled better in these two layeramplification volumes and the excitation for high powers being possiblein a simple way. This is, for example, achieved by the laseramplification volumes being cooled on at least one side and beingirradiated by the high-power source on a side which is not cooled. Onthose sides which are cooled, this cooling can thus be made as effectiveas possible, which enables better removal of the dissipation heat thanin the solutions heretofore. Furthermore, this also allows the laseramplification volume to be excited with higher pumping powers. Finally,use of at least two laser amplifications volumes makes it possible touse a compact design, in particular, a compact structural length, andyet to couple-in the pumping power over a large surface and remove thedissipation heat.

No details were given in the description of the embodiments hereinaboveas to the design of the coupling section. Particularly good coupling isachieved in the coupling section by the coupling section comprising thebeam path of an unstable resonator.

Furthermore, a particularly advantageous, compact geometricalarrangement with best possible imaging characteristics is achieved withthe outer beams lying symmetrically in relation to the coupling axis.

Regarding the design of the mirrors of the coupling section, it isparticularly expedient for the coupling section to comprise one mirrorwhich reflects towards the coupling axis and one mirror which reflectsaway from the coupling axis, with these complementing each other in sucha way that the outer beams are displaced parallel in the directiontowards the coupling axis and imaged towards the latter by the twomirrors.

In the simplest case, provision is made for the mirror reflectingtowards the coupling axis to protrude with its active region in theradial direction away from the coupling axis beyond the active region ofthe mirror reflecting away from the coupling axis and to be acted uponby the outer beams in this protruding region.

In geometrically advantageous solutions, provision is made for thecoupling section to comprise one convex and one concave resonatormirror.

With a view to achieving geometrical relations which are as simple aspossible, it is preferable for the resonator mirrors to be designed andarranged confocally in the coupling section.

In the explanation of the embodiments hereinabove, no details were givenabout the mirrors with which the excitation sections are equipped. In apreferred embodiment, provision is made for the excitation sections tobe closed off by end mirrors on each side facing away from the couplingsection.

These end mirrors preferably reflect the beams in the excitationsections into the coupling section and if a mirror which reflectstowards the coupling axis is used in the coupling section, these beamsstrike this mirror, while the mirror reflecting away from the couplingaxis extends between the beams coming from the excitation sections andpreferably as far as these.

In the description of the embodiments so far, no details were given asto how the laser radiation is to be coupled out of the resonator. Oneadvantageous possibility is for one of the end mirrors to besemitransmissive. As an alternative to this, it is, however, alsoconceivable for both end mirrors to be semitransmissive.

In principle, the end mirrors can be of flat mirror design. However,since the beams of the excitation sections extend over a considerablelength and even diffraction effects cause a beam with a parallel beampath to later expand in the coupling section, provision is preferablymade for the end mirrors to have a curvature which compensates expansionof the beam in the excitation section and reflects the radiation comingfrom the coupling section back into it. Hence expansion of the beams inthe excitation sections can also be compensated with the end mirror andthe resonator thereby made more efficient.

In the event there are two excitation sections, the structurallysimplest solution is to use separate end mirrors. If, however, the endmirrors are to be held in a stable manner, it is advantageousparticularly if a plurality of excitation sections is used, for the endmirrors which close off the excitation sections to be united to a mirrorring.

If, as described hereinabove, the end mirror should expediently alsohave a curvature in order to compensate expansion of the beams in theexcitation sections, provision is preferably made for the mirror to beof toroidal shape.

Particularly advantageous guidance of the beams in the coupling sectionswhich is geometrically desirable as far as the imaging characteristicsare concerned is achieved by the coupling axis being the axis ofsymmetry of the resonator mirrors of the coupling section.

In the even that only two excitation sections are used, provision isexpediently made, for reasons of simplicity, and, in particular, in viewof the advantageous beam shape of the emerging laser beam, for theresonator mirrors of the coupling section to have cylindrical mirrorsurfaces, and, in particular, in this case, the resonator is a cylinderresonator with confocally arranged mirrors.

Within the scope of the inventive solution, it is advantageous, inparticular, to increase the power yet remove the dissipation heatexpediently, to provide several outer beams which are arranged indifferent planes extending through the coupling axis and continuous incorresponding excitation sections.

The planes are preferably arranged at constant angular spacings from oneanother so the outer beams are at constant spacings from one anotherrunning in the azimuthal direction around the coupling axis.

In this case, the resonator mirrors of the coupling section arepreferably of such shape that they have spherical mirror surfaces andextend symmetrically with respect to rotation around the coupling axis.

In arrangement which is advantageous particularly from a geometricalpoint of view, the outer beams form annular segments relative to thecoupling axis.

Insofar as the outer beams which continue in the beams of the excitationsections are spaced from one another in the azimuthal direction aroundthe coupling axis, it is particularly advantageous, in order to achieveoptimum coupling of all outer beams with one another in the couplingsection, for the coupling section to be closed off in the annularsegments which receive no outer beams coming from the excitationsections by mirrors which reflect back. The mirrors which reflect backserve to close off the coupling section completely in the azimuthaldirection so that formation of a beam path radially symmetrically inrelation to the coupling axis in all directions is possible and alldirections are thereby coupled with one another via the coupling axis.

In the simplest case, provision is made for the mirrors which reflectback to be essentially flat mirrors and to thus reflect back theincident rays in the same way as the end mirrors of the excitationsections.

The mirrors which reflect back are preferably positioned such that inthe direction of propagation of the radiation on the coupling sectionside they are arranged before the solid-state rods to thereby enable thespaces between the solid-state rods to be used for cooling these.

A solution wherein the mirrors which reflect back are arranged directlyat the level of one of the mirrors of the coupling section, preferablythe mirror that reflects away from the coupling axis, is particularlyadvantageous.

In a particularly preferred embodiment, in particular to improve thecoupling of the outer beams and to achieve an optimum, compactstructural design, provision is made for the sum of all of the outerbeams to form essentially a closed annulus in the coupling section sothe mirrors which reflect back can be dispensed with.

Particularly when more than two excitation sections are provided, it hasproven expedient for the excitation sections to be arranged axiallysymmetrically around an axis.

Furthermore, in order to simplify the structural design, in particular,a compact structural design, the excitation sections are aligned so asto extend parallel to one another.

To establish correct imaging relations between the coupling section andthe excitation sections, there is preferably provided between thecoupling section and the excitation sections an optical element forimaging the outer beams onto the beams in the excitation sections.

The optical element expediently comprises a cylindrical optical meanwhich, in particular, is of such design that a cylindrical axis of thecylindrical optical means extends in the radial direction.

Such a cylindrical optical means enables optimum exploitation of thecoupling section in the azimuthal direction and, on the other hand,azimuthal spacings which are as large as possible between the laseramplification volumes, namely when the cylindrical optical meanscomprises a cylindrical, optical, annular segment which respectivelyimages the outer beam forming an annular segment in the coupling sectiononto a beam which is narrower in the azimuthal direction in relation tothe coupling axis in the excitation section.

The width of the beam in the azimuthal direction in the excitationsection preferably corresponds at the most to the width of the laseramplification volume in this direction.

A particularly preferred solution within the meaning of the invention isobtained when the cylindrical, optical, annular segments unite to forman annulus and when this annulus comprised of cylindrical, optical,annular segments is capable of imaging an annulus closed by the outerbeams in the coupling section onto a plurality of beams spaced from oneanother in the azimuthal direction in the excitation section so that, onthe one hand, there is a cylindrical-symmetrical beam path in relationto the coupling axis in the coupling section and, on the other hand, thespacings of the beams in the azimuthal direction in the excitationsections enable the laser amplification volumes to be cooled in theregion of these spaces.

In the description of an embodiment of the inventive solutionhereinabove, no details were given as to how the laser amplificationvolumes are to be arranged and designed.

In a preferred embodiment, provision is made for he laser amplificationvolumes to be aligned parallel to one another.

In particular, for geometrical-optical reasons, provision is expedientlymade for the laser amplification volumes to be identical in shape. Inprinciple, the geometry of the laser amplification volumes can beselected optionally. A round or oval cross-section is, for example,conceivable. It is, however, particular advantageous for the laseramplification volumes to be designed as elongate laminae.

To achieve amplification which is as uniform as possible, it is,furthermore, advantageous for the laser amplification volumes to be madeof identical material.

A geometry of the laser amplification volumes has, however, provenparticularly advantageous wherein the laser amplification volumes havetwo broad sides facing each other, with the spacing of the broad sidespreferably being selected such that optimum heat removal of thedissipation heat from the laser amplification volumes can take place inthe direction of the broad sides.

It is furthermore, advantageous for the laser amplification volumes tohave two narrow sides facing each other, with the spacing of the narrowsides being selected such that it is essentially of the order ofmagnitude of a penetration depth of the pumping power so coupling-in ofthe pumping power preferably takes place via the narrow sides.

The type of the laser amplification volume was not specified in any ofthe inventive solutions described hereinabove. In an advantageousembodiment the layer amplification volume is formed by a solid-staterod.

This solid-state rod is preferably optically excitable and, inparticular, the pumping means irradiates the solid-state rod from oneside.

An embodiment wherein the pumping power impinges upon a narrow side isparticularly simple.

In this case, it is then likewise advantageous for at least one broadside to be cooled.

The broad sides are preferably flat surfaces. It is similarly expedientfor the narrow sides, in particular the narrow side on which the pumpingpower impinges, to also be designed as flat surfaces.

In the simples case, it is advantageous for the solid-state rods to havean essentially four-cornered cross-section, with the two broad sidesextending essentially perpendicular to the two narrow sides.

Particularly advantageous cooling of the solid-state rod is possiblewhen the solid-state rod is cooled on both broad sides. Optimum coolingof the solid-state rod is possible when the solid-state rod isadditionally cooled on a narrow side and coupling-in of the pumpingpower, therefore, takes place on one narrow side only.

The description of the embodiments hereinabove contains no details ofthe type of cooling. It has proven particularly advantageous for thesolid-state rods to be cooled by contact with a flow-free material,i.e., for cooling to take place by direct thermal contact with anelastic or plastic substance or a rigid body, it also being possible, inthe even a rigid body is used as cooling element, for an elastic orplastic substance to serve as heat-transmitting medium between thecooling element and the solid-state rod.

In general, if such contact cooling is used, it is advantageous for thesolid-state rods to be cooled on their sides facing one another so thesolid-state rods can, for example, be acted upon the pumping power ontheir sides facing away from one another.

In particular if the excitation sections are arranged axiallysymmetrically in relation to an axis, provision is expendiently madefrom the solid-state rods to be cooled on a side extending approximatelyin the direction towards a radius direction of the axis.

In accordance with the invention, the most advantageous cooling isenabled by the solid-state rods being cooled by contact with a coolingelement, with the cooling element preferably resting on two sides of thesolid-state rod facing each other.

In this case, to avoid a heat-transmitting medium in the form of anelastic or plastic material, provision is preferably made for thecooling element to rest with a press fit on the solid-state rod, withthe press fit preferably being established by the contact with the twosides of the solid-state rod facing each other.

In principle, it is possible to allocate to each solid-state rod acooling element of its own. It is, however, particularly advantageousfor the cooling element to lie between the solid-state rods of theexcitation sections which belong to one another.

Furthermore, the cooling element also makes it possible for it to bedesigned so as to carry the solid-state rods so that fixing of thesolid-state rods by additional holding means is not necessary but at thesame time cooling of the solid-state rod also takes place via theseholding means.

In a particularly preferred solution, provision is made for thesolid-state rod to sit with both broad sides and one narrow side in agroove of the cooling element.

Details have also not been given about the material from which thecooling element should be made. It is advantageous for the coolingelement to be made of a material with good heat conductivity, and it ispreferable for the cooling element to be a metal element.

To keep the cooling element at a constant temperature, it is expedientfor a cooling medium to flow through the cooling element.

In the description of the embodiments hereinabove, it was not explainedin detail how the solid-state rods are acted upon by the pumping power.In a particularly preferred solution, provision is made for thesolid-state rods to be acted upon with pumping power on their sidesfacing away from one another. Such a solution provides the optimumgeometrical possibilities for introducing as much pumping power aspossible into the solid-state rods. In all of the embodiments in whichthe excitation sections are arranged axially symmetrically around anaxis, this is achieved by the solid-state rods being irradiated by thepumping power source on a side surface extending essentiallytransversely to a radius direction of the axis. This makes it possiblefor the solid-state rods to be acted upon with pumping power in theradial direction in relation to the axis away from this axis or in theradial direction in relation to the axis towards this axis. It hasproven particularly advantageous for the solid-state rods to be actedupon with the pumping power in the radial direction of the axis towardthe latter.

Moreover, in all the embodiments in which the solid-state rods arecooled by the cooling element, the solid-state rods can beadvantageously acted upon with the pumping power by each solid-state rodbeing acted upon by the pumping power on its side surface which is notencompassed by the cooling element.

In combination with the arrangement of the cooling element, the mostadvantageous geometrical arrangement of cooling element and pumpingpower source is for the cooling element to be surrounded by the pumpingpower source. In this case, the pumping power source is expendientlydesigned so as to radiate in an essentially radial direction onto thecooling element.

To enable the pumping power to be coupled into the solid-state rods aseffectively as possible, it is expedient for elements which concentrateon the solid-state rods to be provided for the pumping power.

These concentrating elements are preferably designed to deflect onto thesolid-state rods electromagnetic radiation emitted by the pumping powersource into a solid angle.

One possibility of providing such concentrating elements is to providean optical refraction means, for example, in the form of a cylindricallens between the pumping power sources and the solid-state rods.

It is, however, even more advantageous for the concentrating elements tobe reflectors which can be arranged on a side of the pumping powersource facing the respective solid-state rod or between the pumpingpower source and the respective solid-state rod.

In a particular good combination of the concentrating elements with thecooling element, provision is made for the intermediate webs of thecooling elements to pass on the pumping power impinging thereon to thesolid-state rods, it being possible for this passing-on to beimplemented in a variety of different ways.

Here, it has, however, proven particularly advantageous for theintermediate webs to comprise surfaces which reflect the pumping powerto the solid-state rods.

In the simplest case, the intermediate webs are designed so as to risein tapering configuration above the solid-state rods, the simplestsolution from a manufacturing viewpoint being that of the intermediatewebs tapering in wedge-shaped configuration.

Within the scope of the present invention, a very wide variety ofsolutions is likewise conceivable for the type of design of the pumpingpower source.

In a particularly preferred embodiment, provision is made for thepumping power source to surround the solid-state rods in annularconfiguration.

In this case, the pumping power source is preferably a gas-dischargelamp.

Such a gas-discharge lamp can be operated in many different ways. In apreferred embodiment, provision is made for a gas discharge to begenerated in the gas-discharge lamp by a field extending essentiallyradially in relation to its axis.

It is however, also conceivable for a gas discharge to be generated inthe gas-discharge lamp by a field extending azimuthally in relation toits axis, the gas-discharge lamp being divided by electrodes intoannular segments for this purpose.

It is particularly advantageous for the gas discharge to be generated byhigh frequency in the gas-discharge lamp, with the high frequency thenbeing applied by electrodes spaced in the radial or azimuthal direction.

As an alternative to this, it is, however, also conceivable, instead ofusing electrodes, for the high frequency to be coupled into thegas-discharge lamp in the form of microwaves.

A further alternative to the coupling of the high frequency into thegas-discharge lamp is inductive coupling of the high frequency into thegas-discharge lamp.

As an alternative to provision of a single pumping power source, it is,however, likewise conceivable to arrange a plurality of single pumpingpower sources around the cooling element, the single pumping powersources being arranged, in particular, alongside one another. In thesimplest case, the single pumping power sources are likewisegas-discharge lamps with the gas discharge preferably being generated byhigh frequency with one of the types of coupling-in mentionedhereinabove.

As an alternative to this it is, however, also conceivable for thesingle pumping power sources to be designed as rows of laser diodeswhich have the advantage of an emission characteristic concentrated on asmall solid angle.

As an alternative to the variant of the solid-state laser describedhereinabove with an optically pumped solid-state rod, provision islikewise preferably made in the inventive solution for the laseramplification volume to be that of a semiconductor layer and, in thiscase, the laser-active unit is formed by a semiconductor laser means ofcommonly known design. In such a semiconductor laser, provision is madefor several laser-active regions to be provided in each layeramplification volume. Herein the laser-active regions are thelaser-amplifying semiconductor layer regions of a semiconductor laser.

In the inventive use of a semiconductor laser as laser-active units,provision is preferably made for the laser-active regions to be seatedbetween semiconductor layers of the pumping means forming a pn-junction.

These laser-active regions are preferably of strip-shaped design and, inparticular, arranged in spaced relation to one another to make ispossible for these laser-active regions to be supplied with sufficientcooling power.

In an expedient arrangement, provision is made for the laser-activeregions to extend parallel to one another.

In this case, laser-inactive regions are preferably arranged in spacesbetween the layer-active regions so that laser-active and laser-inactiveregions alternate with one another in a layer.

In one variant which allows the beam to run in a disturbance-free mannerin such a laser excitation volume, provision is preferably made for thelaser-inactive regions to be of transparent design for the beam, inparticular, to be made of transparent material.

Herein the laser-inactive regions are preferably in the form ofsemiconductor layer regions but with an increased ban gap with respectto the laser-active regions so that there is no absorption of the laserradiation in the laser-inactive regions.

Since in such an embodiment of the inventive solution the beampenetrates partly laser-active and partly laser-inactive regions,problems arise when the laser-inactive regions and the laser-activeregions do not have the same index of refraction. In this case, thearrangement of the laser-active and laser-inactive regions represents aphase grid for the beam. Hence in the event the laser-active andlaser-inactive regions do not have the same index of refraction, it isadvantageous for the optical length of the laser-active andlaser-inactive regions to be of such dimensions that the parts of thebeam penetrating these have the same phase position so that the maximumintensity lies in the zeroth order of the phase grid.

As an alternative to the solution in which the laser-inactive regionsare made of transparent material, provision is made in a furtherinventive solution for the laser-inactive regions to be material-freechannels so that no problems can arise with the absorption in theselaser-inactive regions.

However, in this case the indexes of refraction differ between thelaser-active and laser-inactive regions so that the optical length ofthe laser-active and laser-inactive regions is advantageously of suchdimensions that the parts of the beam penetrating these differ in phaseby an integral multiple of 2π.

In a particularly preferred embodiment of the inventive solution, it isadditionally advantageous for the same partial beam, imaged as beams, topenetrate two laser amplification volumes of two laser-active unitswhich are arranged one after the other in the direction of propagationof the beams so that a further power increase is thereby possible.

Herein the laser-active units are advantageously arranged eitherimmediately one behind the other or in the form of two excitationsections which are arranged one behind the other and between whichimaging into a partial beam again takes place.

In the cases where the laser-active units are arranged immediately onebehind the other, it is possible for the laser-active and laser-inactiveregions to be in alignment with one another. It is, however, alsopossible for the laser-active regions to be arranged in offset relationto one another so that, for example, a laser-inactive region of alaser-active unit is in alignment with the laser-active region of theother laser-active unit or the laser-active regions are offset inrelation to one another in the transverse direction.

In particular, such arrangements are also advantageous with excitationsections which are arranged in succession. Herein a further advantageousvariant is made possible by the laser-active units being turned withrespect to one another, preferably through an angle of 90°, about anaxis parallel to the direction of propagation.

Furthermore, an advantageous embodiment makes provision for severallaser-active units to be arranged alongside one another in sandwich-likeconfiguration. It is particularly advantageous for several laser-activeunits to form a laser-active block.

The pumping means is preferably connected to a cooling element so thatthe laser-active regions are preferably pumped and cooled from sidesfacing one another.

The cooling element is expediently designed so as to comprise at leastone heat-conducting layer.

The pumping means and the cooling element are preferably integrated intothe laser-active unit and arranged as such in an excitation section.

Further features and advantages of the invention are the subject matterof the following description and the appended drawings of severalembodiments. The drawings show:

FIG. 1 a plan view of a first embodiment;

FIG. 2 a section along line 2--2 in FIG. 1;

FIG. 3 a section through a second embodiment;

FIG. 4 a section along line 4--4 in FIG. 3;

FIG. 5 a section along line 5--5 in FIG. 3;

FIG. 6 a section through a third embodiment;

FIG. 7 a partial section along line 7--7 in FIG. 6;

FIG. 8 an angled, planar illustration of the partial section in FIG. 7;

FIG. 9 a section along line 9--9 in FIG. 6;

FIG. 10 a partial section of a variant of the third embodiment;

FIG. 11 a section similar to FIG. 9 through a second variant of thethird embodiment;

FIG. 12 a section similar to FIG. 3 through a fourth embodiment;

FIG. 13 a section along line 13--in FIG. 12;

FIG. 14 an enlarged sectional illustration similar to FIG. 13 through alaser-active unit;

FIG. 15 an enlarged plan view of a variant of a laser-active unit;

FIG. 16 an enlarged plan view similar to FIG. 15 of a further variant ofa laser-active unit;

FIG. 17 a plan view of a fifth embodiment;

FIG. 18 a section along line 18--18 in FIG. 17;

FIG. 19 an enlarged illustration of areas A and B in FIG. 17;

FIG. 20 a partial illustration of a section similar to FIG. 18 through avariant of the fifth embodiment;

FIG. 21 a sectional illustration similar to FIG. 20 through a furthervariant of the fifth embodiment;

FIG. 22 a plan view similar to FIG. 17 of a sixth embodiment; and

FIG. 23 a second along line 23--23 in FIG. 22;

FIG. 24 a plan view similar to FIG. 22 of a seventh embodiment.

A first embodiment of an inventive solid-state laser, illustrated inFIG. 1, comprises a resonator designated in its entirety 12 andcomprising a first excitation section 14 and a second excitation section16 which are both arranged parallel to one another and symmetrically inrelation to an axis 18 and each comprise a path of rays with a parallelbeam 20 and 22, respectively, and so the beams 20 and 22 also extendparallel to one another and symmetrically in relation to the axis 18.

These beams 20 and 22, respectively, enter as outer beams 24 and 26,respectively, a coupling section designated in its entirety 28 of theresonator 12 symmetrically in relation to a coupling axis 30 and arereflected in the coupling section by reflection in the direction of thecoupling axis 30, preferably imaged towards the coupling axis 30, so thecoupling between the two outer beams 24 and 26 beyond the coupling axis30 results in the joint beam 31.

The two outer beams 24 and 26 thereby form a coupling plane extendingthrough the coupling axis 30 and are reflected by the coupling section28 of the resonator 12 in this coupling plane towards the coupling axis30 in order to couple with one another beyond the coupling axis 30 toform the joint beam 31.

Owing to this design of the resonator 12, the first excitation section14 and the second excitation section 16 are completely coupled with oneanother and so coherent laser radiation forms in these two excitationsections 14 and 16 beyond the coupling section 28.

The first excitation section is preferably closed off on a side oppositethe coupling section 28 by an end mirror 32 and the second excitationsection 16 by an end mirror 34, these preferably being flat mirrors bothlying in a plane 36 perpendicular to the axis 18.

The coupling section 28, in turn, is preferably formed on its sideopposite the excitation sections 14 and 16 by a concave mirror 38 and onits side facing the excitation sections 14 and 16 by a convex mirror 40.The convex mirror 40 extends between the two outer beams 24 and 26 whichpropagate as straight-line continuation of the beams 20 and 22 into thecoupling section 28 past the sides of the convex mirror 40 and impingeupon the concave mirror 38 which reflects onto the convex mirror 40which then reflects back again to the concave mirror 38, moreparticularly, parallel to the outer beams 24 and 26. This results inreflection back and forth of the beams 24 and 26 until these reach thecoupling axis 30 and pass over the 34 latter into the respective otherbeam 26 and 24, respectively.

The concave mirror 38 and the convex mirror 40 are preferably designedas the two mirrors of a cylinder resonator, in particular, a confocalcylinder resonator, the resonator axis of which is the coupling axis 30.

It is preferably for both the concave mirror 38 and the convex mirror 40to have cylindrical mirror surfaces 42 and 44 which are curved in thedirection of the coupling plane, but are preferably not curvedperpendicular to the coupling plane.

In the case of a cylinder resonator formed by mirrors 38 and 40, theresonator axis is that axis which stands perpendicular on both mirrorsurfaces 42 and 44.

The excitation sections 14 and 16 each contain a solid-state rod 46 and48, respectively, which with a longitudinal axis parallel to a firstdirection 50 and 52, respectively, each extend parallel to the axis 18,with each solid-state rod 46 and 48, respectively, being completelypermeated by the respective beam 20 and 22, respectively.

For coupling the laser radiation out of the resonator 12, the end mirror32, for example, is designed as semi-transmissive mirror which thusreflects the beam 20 only partly and from which there emerges acoupled-out beam 54 which is expanded to a beam with a squarecross-section by a cylindrical optical means 56.

It is, however, also conceivable for both the end mirror 32 and the endmirror 34 to be of semitransmissive design and for two coupled-out beamsto be allowed to emerge from the resonator 12. As illustrated in FIG. 2,the solid-state rods 46 and 48 are designed as rods with a rectangularcross-section, each solid-state rod having two broad sides 60 and 62facing each other and two narrow sides 64 and 66 facing each otherwhich, in accordance with the invention, are formed by flat surfaces,with the broad sides 60 and 62 extending perpendicular to the narrowsides 64 and 66.

Each solid-state rod 46 and 48 is, for its part, held in a coolingelement designated in its entirety 68 which engages over eachsolid-state rod 46 and 48, respectively, on both broad sides 60 and 62and preferably also on the narrow side 66 facing the axis 18 and restsin a thermally contacting manner on the two broad sides 60 and 62 andpreferably also on the narrow side 66.

With the narrow side 64 facing away from the axis 18, each of thesolid-state rods 46 and 48 faces a light source 70 and 72, respectively,acting as pumping power source, In the simplest case, the light sources70 and 72 are gas-discharge lamps. Each of the solid-state rods 46, 48forms with the respective light source 70 and 72, respectively, alaser-active unit 73.

These light sources 70 and 72 are preferably designed so as to emittheir light in the form of pumping radiation 74 and 76, respectively,essentially in the direction of the narrow side 64 so the pumpingradiation can penetrate the respective solid-state rod 46 and 48,respectively, via the respective narrow side 64, the spacing of thenarrow side 64 from the narrow side 66 preferably being selected in theorder of magnitude of the penetration depth of the pumping radiation 74and 76, respectively, in order that the pumping radiation 74 and 76,respectively, will penetrate the solid-state rod 76 and 48,respectively, over its entire expanse in the direction of the broadsides 60 and 62 and hence excite these to an essentially full extent.

In order to also use diverging pumping radiation 74 and 76,respectively, coming from the light sources 70 and 72 as fully aspossible for excitation of the respective solid-state rod 46 and 48,respectively, the cooling element 68 is additionally provided withreflector surfaces 78 and 80, respectively, which, in accordance withthe invention, extend from each solid-state rod, starting at the levelof the respective narrow side 64 on the respective broad sides 60 and62, respectively, away from the axis 18 with increasing spacing from oneanother and preferably at an acute angle and symmetrically in relationto a center plane 82 which, for its part, extends through the axis 18and through the light source 70 as well as through the center of therespective solid-state rod 46 and 48, respectively. By means of theseexpanding reflector surfaces 78 and 80, respectively, pumping radiation74 propagating at an acute angle to the center plane 82 is alsoreflected towards the respective solid-state rod 46 and 48,respectively, and hence used to excite the latter.

The spacing of the broad sides 60 and 62 is chosen in accordance withthe heat conductivity of the solid-state rods 46 and 48, respectively,more particularly, such that the heat to be removed from thesesolid-state rods 46 and 48, respectively, can be conducted away quicklyenough for it not to cause excessive heating-up of the solid-state rods46 and 48, respectively, and hence the known problems caused by thethermal expansion of the solid state rods 46 and 48 no longer occur.

To achieve optimum heat transfer from the broad sides 60 and 62 to thecooing element 68, the solid state rods 46 and 48, respectively, arepreferably clamped into the cooling element between two side webs 84 and86, respectively, which thus rests with pressure on the broad sides 60and 62. The heat conductivity between the solid-state rods 46 and 48 canbe additionally improved by a heat conducting agent, for example, a heatconducting paste being applied between the side webs 84 and 86 and thebroad sides 60 and 62.

Optimum thermal contact can be established between the narrow side 66and the cooling element 68 in the same way. For this purpose, a groovedesignated in its entirety 88 is preferably provided between the sidewebs 84 and 86, with the narrow side 66 resting on the groove bottom 90thereof.

To improve the illumination of the solid-state rods 46 and 48,respectively, a contact surface 92 and 94 of the side webs 84 and 86 ispreferably a reflecting design and hence serves as continuation of therespectively reflector surface 78 and 80, respectively, so that all ofthe pumping radiation 74 and 76, respectively, reflected by thereflector surfaces 78 and 80, respectively, into the groove 88 is alsoreflected back and forth by these contact surfaces 92 and 94,respectively, and hence optimum illumination of the solid-state rods 46and 48, respectively, takes place over their entire cross-section.

For optimum removal of the heat into the cooling element, the latterpreferably contains cooling channels 96 preferably extending in thelongitudinal direction of the cooling element 68, i.e., parallel to theaxis 18, and near the contact surfaces 92 and 94 as well as the groovebottom 90.

A good heat conducting material, i.e., for example, copper is used aspreferred material for the cooling element 68.

Ruby or neodymium and, for example, also titanium sapphire arepreferably used for the solid-state rods 46 and 48, respectively, ofthis inventive solid-state laser.

A second embodiment of an inventive solid-state layer, illustrated inFIGS. 3 to 5, is, in principle, of exactly the same design as the firstembodiment. In particular, a resonator 112 thereof is likewise providedwith a first excitation section 14 and a second excitation section 16both lying with their beams 20 and 22 in a plane which in the couplingsection 28 is a coupling plane over which the outer beam 24 couples withthe outer beam 26. In contrast with the first embodiment, however, notonly two excitation sections 14 and 16 are provided, but instead aplurality of planes 114, 116, 118 and 120 which all extend through theaxis 18 and through the coupling axis 30 coaxial with the latter andform a family of planes in relation to the axis 18.

Arranged in each of these planes 114, 116, 118 and 120 are a firstexcitation section 14 and a second excitation section 16 with theirbeams 20 and 22.

The coupling section 28 likewise comprises the concave mirror 38 and theconvex mirror 40, with the concave mirror 38 having a spherical concavemirror surface 122 and the convex mirror 40 and a convex sphericalmirror surface 124, and the mirror surfaces 122 and 124 likewise lyingconfocally in relation to each other. Hence the coupling section 28forms a spherical unstable resonator which couples the outer beams 24and 26 of the respective planes 114, 116, 118 and 120 with one another,but also in the region of the coupling axis 30 the beams of theindividual planes 114, 116 and 120 with one another so that, in all, ajoint beams 121 with coherent radiation is formed in the resonator 112with a plurality of first and second excitation sections 14, 16 and witha coupling section 28.

The end mirrors 32 and 34 of the first and second excitation sections 14and 16 are preferably all of semitransmissive design so that a pluralityof coupled-out beams 126, all arranged axially symmetrically in relationto the axis 18 around the latter, emerges from the resonator 112.

To improve the coupling of the radiation propagating in the respectiveplanes in the resonator 112 between the planes 114, 116, 118 and 120,there is arranged between the coupling section 28 and the excitationsections 14 and 16 a mirror element 128 which, as illustrated in FIG. 5,by means of non-reflective sectors 130, 132, 134 and 136 allows thebeams 24 and 26 in the respective planes 114, 116, 118 and 120 to pass,but between these sectors 130, 132, 134 and 136 comprises mirroredsectors 138, 140, 142, and 144 which close off the coupling section 28in the sector regions between the beams 24 and 26 in order to alsopermit radiation propagation in these regions in the coupling section 28and hence optimally couple all outer beams 24 and 26 with one another.The mirrored sectors 138, 140, 142 and 144 are preferably likewise flatmirrors which reflect back in the same way as the end mirrors 32 and 34which are likewise preferably designed as flat mirrors, in order to alsoensure between the outer beams 24 and 26 in the coupling section 28 aparallel path of rays which can thus circulate in the azimuthaldirection and pass over into the parallel path of rays of the outerbeams 24 and 26.

In the second embodiment, the planes 114, 116, 118 and 120 arepreferably arranged at constant angular spacings relative to one anotherso that the axis 18 and the coupling axis 30 form multiple axes ofsymmetry for the path of rays in the resonator 112.

As illustrated in FIG. 4, the cooling element 146 is arranged ascylinder coaxially with the axis 18 and comprises grooves 88, with theplanes 114, 116, 118 and 120 forming center planes corresponding to thecenter plane 82 for the arrangement of the solid-state rods 46 and 48and the arrangement of the light sources 70 and 72. Furthermore,reflector surfaces 78 and 80 are provided in the same way as i the firstembodiment, and the reflector surfaces 88 and 78 form successive points148. In this embodiment, the solid-state rods 46 and 48 are preferablyof trapezoidal design, with the broad sides 60 and 62 lying in radialplanes extending through the axis 18, while the narrow sides 64 and 66extend parallel to one another.

For a description of parts of the second embodiment which have the samereference numerals as those of the first embodiment and hence areidentical with these with respect to function, reference is to be had tothe description and explanation of the function of the first embodiment.

In a third embodiment, illustrated in FIGS. 6 to 9, those partsidentical with those of the first and second embodiments have the samereference numerals and so insofar reference is to be had to thedescription of the first and second embodiments.

In contrast with the second embodiment, as illustrated in FIGS. 7 and 9,a large number of planes 150 corresponding to the planes 114 to 120 isprovided. These all form a family of planes extending through the axis18 and the coupling axis 30 and are at identical angular spacing fromone another, and a first and a second excitation section 14 and 16 withsolid-state rods 46 and 48, respectively, and beams 20 and 22,respectively, lie in each plane 150.

The resonator 152 comprises in the same way as the resonator 112 aplurality of beams 20 and 22 which are coupled with one another by thejoint beam 121 in the coupling section 28 provided with spherical mirrorsurfaces 122 and 124 via a coupling axis 30 and so in this connectionreference is to be had in full to the explanations of the first andsecond embodiments.

In contrast with the second embodiment, however, the mirror element 128is replaced by an imaging element 154 illustrated in FIGS. 6, 7 and 8which, as illustrated in FIGS. 7 and 8, comprises a plurality ofcylindrical optical segments 156 seated alongside one another anddesigned in the form of adjoining annular segments in relation to theaxis 18.

Each of these cylindrical optical segments 156 is designed symmetricallyin relation to the respective plane 150 and has a convex cylindricalsurface 158 facing the coupling section 28 and a concave cylindricalsurface 160 facing the respective excitation section 14 and 16,respectively, the two cylindrical surfaces 158 and 160 having such acurvature that a parallel, outer beam 24 and 26, respectively, forming apartial beam of the joint beam 121 and having the shape of an annularsegment is narrowed in the azimuthal direction 162 and hence forms thecorresponding beam 20 and 22, respectively, which thus extends in theazimuthal direction 162 to a likewise parallel beam over a smallerangular area, and, conversely, a beam 20 extending over a smallerangular area in the azimuthal direction 162 is expanded by thecylindrical surfaces 160 and 158 to an outer beam 24 extending over alarger angular area in the azimuthal direction 162.

Since all of the cylindrical optical segments 156 are preferablydesigned such that the convex cylindrical surfaces 158 adjoin oneanother, the path of rays in the resonator 152 can be selected such thatall outer beams 24 and 26, respectively, of successive planes 150 touchone another and hence the coupling section 28 comprises beams 24 and 26,respectively, which follow one another directly and adjoin one anotheras they circulate in the azimuthal direction 162. On the other hand, ashorter extent of the beams 20 and 22, respectively, in the azimuthaldirection 162 is achieved with the cylindrical optical segments 156 andso spaces 164 remain between the successive beams 20 and 22,respectively. As a result of this, there also remain between thesolid-state rods 46 and 48 located in the respective planes 150 spacesin which the side webs 84 and 86 of the cooling element 166 enclosingthe solid-state rods 46 and 48 between them are arranged, the coolingelement 166 being of similar design to the cooling element 146, buthaving grooves 88 which lie closer together so as to permit a largernumber of planes 150.

In a modification of the first and second embodiments, as illustrated inFIG. 6, the end mirrors 32 and 34 of the excitation sections 14 and 16are, furthermore, united to form an annular end mirror 168 comprisingmirror surfaces 172 curved in the radial direction 170 in relation tothe axis 18, the curvature of the mirror surfaces 172 being toroidal.The curvature of the mirror surfaces 172 is selected such that itcompensates a slight expansion of the beams 20 and 22 in the radialdirection 170 caused by diffraction effects in the coupling section 28by reflecting each incident ray of the beams 20 and 22, respectively,back into itself and hence keeping the outer beams 24 and 26 parallel inthe coupling section 28.

In contrast with the first and second embodiments, there is preferablyprovided in the third embodiment, as illustrated in FIG. 9, a single,for example, cylindrical light source 174 which, in particular, can be acylindrical discharge lamp arranged coaxially with the axis 18. This ispreferably also cooled by a cylindrical cooling jacket 176 which isarranged on the side of the light source 174 facing the cooling element166 and, in the simplest case, comprises a coolant 182 conducted betweenan outer cylinder wall 178 and an inner cylinder wall 180, the coolant182 being constantly exchanged and externally cooled.

In the simplest case, the light source 174 is a gas discharge lamp withthe gas discharge which takes place being initiated by an electric fieldstrength extending in the radial direction 170.

For the purpose, the light source 174 is provided with an outerelectrode 184 and, on the other had, the cooling element 166 canrepresent the inner electrode.

The light source 174 forms with each of the solid-state rods alaser-active unit 73.

In contrast with the gas discharge by means of a radial, electric field,it is, however, also conceivable for the light source 174, asillustrated in FIG. 10, to be divided up into flat electrodes 186 and188 which are arranged in the radial direction 170 and between which anelectric field strength oriented in the azimuthal direction 162 can begenerated in order to initiate therein a gas discharge in agas-discharge space 190 of the light source 174', this gas dischargepreferably being a high-frequency gas discharge.

As an alternative to this, it is also possible for the electrodes 186and 188 to be omitted and for a gas discharge to then be initiated tocouple microwaves to the gas-discharge space 190.

In a further variant of the inventive solution, illustrated in FIG. 11,the reflection surfaces 78 and 80 are drawn from the cooling element 166up to a row of semiconductor diodes 192, with the row of semiconductordiodes 192 extending parallel to the axis 18, preferably essentiallyover the length of the solid-state rods 46 and 48, respectively, in thisdirection. The reflection surfaces 78 and 80 serve to radially conductthe light emitted from the respective row of semiconductors 192 in thedirection towards the respectively associated solid-state rod 46 and 48,respectively, so that essentially the total light emitted from thesemiconductor diode 192 is guided to the respective solid-state rod 46and 48, respectively, and serves to excite the latter.

Semiconductor diode rows 192 are preferably arranged in the azimuthaldirection 162 around the entire cooling element 166, with their lightbeing guided from the respective reflection surfaces 78 and 80,respectively, to the respective solid-state rod 46 and 48, respectively.

The resonator concepts described on the basis of resonators 12, 122 and152 could also be modified within the scope of the present invention,for example, the scope of the present invention also allows use ofresonator concepts as described in the article "Unstable resonators forannular gain volume lasers" in APPLIED OPTICS, Volume 17, No. 6, Mar.15, 1978, to which references is expressly made in this connection.

In a fourth embodiment of an inventive solid-state rod, illustrated inFIGS. 12 and 13, the resonator 212 is identical in design to theresonator 112 of the first embodiment and, in addition, the excitationsections 14 and 16 as well as the beams 20 and 22 are arranged in thesame way, with two excitation sections 14 and 16 likewise lying in eachof the planes 114, 116, 118 and 120.

Moreover, the coupling section 28 is also of identical design andcomprises the beams 24 and 26 as well as the coupling axis 30.Therefore, in this connection reference is to be had in full to thestatements on the second embodiment.

Furthermore, the concave mirror 38 is also provided in the same way asin the second embodiment with a spherical concave mirror surface 122 andthe convex mirror 40 with a convex spherical mirror surface 124. Aslikewise described in detail in connection with the second embodiment,these cooperate with one another to couple the beams 24 and 26 of therespective planes 114, 116, 118 and 120 with one another to form thejoint beam 121.

In addition, the end mirrors 32 and 34 are also designed in the same wayas in the second embodiment so that a plurality of coupled-out beams 126likewise form in axially symmetrical relation to the axis 18 and emergefrom the resonator 212.

Finally, the mirror element 128 also acting in the same way as in thesecond embodiment is provided for coupling the radiation which builds upthe resonator 212 and so reference is also to be had in this connectiongo the statements on the second embodiment.

The fourth embodiment differs from the second embodiment in that insteadof the solid-state rods 46 and 48, laser-active units 214 in the form ofsemiconductor lasers are now seated in the grooves 88 of the coolingelement 146.

As illustrated in FIGS. 13 and 14, each of the laser-active units 214comprises a laser amplification volume 216 with a pumping meansdesignated in its entirety 218 adjoining it on either side thereof. Thispumping means 218 comprises in sandwich-like configuration semiconductorlayers 220 and 222 of a pn-junction which enclose the laseramplification volume 216 between them and on which there is positionedas contact and cooling area a metal layer 224 and 226, respectively,facing the laser amplification volume 216. The power supply leads to themetal layers 224 and 226.

The laser-active unit 214 is preferably a semiconductor laser in theform of a gallium arsenide laser so that the semiconductor layer 222 is,for example, the p-gallium arsenide layer, the semiconductor layer 220the n-gallium arsenide layer and the metal layer 226 is supplied withthe positive supply voltage and the metal layer 224 with the negativesupply voltage.

In the simplest case, the laser amplification volume 216 could be acontinuous laser-active layer lying between the semiconductor layers 220and 222 with its band gap being lowered with respect to the adjacentlayers by additional aluminum doping and hence having the lowest bandgap. However, in such a case there are problems with the heatdissipation and so the layer amplification volume 216 preferablycomprises strip-shaped laser-active regions 228 extending in a firstdirection 230 parallel to the longitudinal direction 21 and 23 of thebeams 20 and 22, respectively.

Arranged between the laser-active regions 228 are laser-inactive regions232 which in one variant likewise represent a semiconductor layer whoseband gap is preferably selected such that this semiconductor layer doesnot absorb the laser radiation propagating in the respective beam 20 and22, respectively, i.e., that the band gap of the semiconductor layer isgreater than the band gap in the laser=active region. The laser-inactiveregions 232 preferably extend between the laser-active regions 228likewise in strip-shaped configuration in the first direction 230.

Hence the laser amplification volume in the embodiment of thelaser-active unit 214 illustrated in FIG. 14 is formed by the sum of thelaser-active regions 228 and the laser-inactive regions 232 which bothextend in the first direction 230.

In the embodiment of the laser-active unit 214 illustrated in FIG. 14,the laser-active regions 228 and the laser-inactive regions 232 are thesame length and so the laser-active unit comprises a front side 234representing one plane and in the same way a rear side, not illustratedin the drawing, extending parallel to the front side 234. The front side234 preferably extends perpendicular to the first direction 230.

The strip-shaped laser-active regions 228 are of such dimensions thattheir narrow side 236 extending between the semiconductor layers 220 and222 has approximately and expanse of 1 μm and their broad side 238extending perpendicular, i.e., parallel to the semiconductor layers 220and 222, an expanse of approximately 2 μm. Furthermore, the strip-shapedlaser-active regions 228 extending the first direction 230 over adistance of the order of 1 mm.

The narrow side 240 of the laser-inactive regions 232 also has theexactly the same width as the narrow side 236 of the laser-activeregions 228, and a broad side 242 of the laser-inactive regions is ofsuch dimensions that it has an expanse of the order of 5 μm.

The total expanse of the laser amplification volume 216 parallel o thebroad sides 238 and 242 in the direction of a height 244 of the laseramplification volume 216 is of the order of 10 mm and so acorrespondingly large number of laser-active regions 228 andlaser-inactive regions 232 alternate with one another.

The laser-active units 214 are seated in the grooves 88 such that therespective layer amplification volume 216 is penetrated by the beams 20and 22, respectively, with the beams 20 and 22, respectively, extendingwith their directions of propagation 21 and 23, respectively, parallelto the first direction 230 of the respective laser-active unit 214.Furthermore, the beams 20 and 22, respectively, have such an expanse ina transverse direction 25 to its direction of propagation 21, 23 thatthey extend within the laser amplification volume 216 and hence betweenthe semiconductor layers 220 and 222, the width of the narrow sides 236and 240, respectively, of the laser-active regions 228 and thelaser-inactive regions 232, respectively.

The fourth embodiment operates by the beam 20 and 22, respectively,penetrating the laser amplification volume 216, with laser amplificationbeing imparted to the segments of the beams 20 and 22, respectively,passing through a laser-active region 228, whereas no laseramplification is imparted to the other segments passing through thelaser-inactive regions 232. Averaged over the respective beam 20 and 22,respectively, the laser amplification is, however, so great that theemerging laser beam has the power of a high-power laser.

Owing to the small dimensions of the successive laser-active regions 228and laser-inactive regions 223, these act like a phase grid extending inthe direction of the height 244 for the beam 20 and 22, respectively,passing through the laser amplification volume 216. For this reason, thelaser-active regions 228 and the laser-inactive regions 232 arepreferably made of a semiconductor material which has a similar index ofrefraction. Furthermore, the extent of the laser-active regions 228 andthe laser-inactive regions 232 in the direction of the first directionis preferably such that the segments of the respective beams 20 and 22,respectively, passing through these move through the same optical pathlength so that these have the same phase position after passing throughthe laser-active regions 228 and the laser-inactive regions 232.

This is either achievable with a planar front side 234 and a planar rearside by the extent of the laser-active regions 228 and thelaser-inactive regions 232 in the direction of the first direction 230being selected accordingly.

Or, alternatively, with the laser=active unit 214' of the variant of thefourth embodiment, illustrated partially and on an enlarged scale inFIG. 15, the constant phase position of the segments of the beam 20 and22, respectively, penetrating the laser-active regions 228' and of thesegments of the beams 20 and 22, respectively, penetrating thelaser-inactive regions 232' is achievable by these segments having adifferent length in the first direction 230. This is achievable by, forexample, the front side 234 no longer being one plane but, for example,having grooves 248 lying between the laser-active regions 228' so thatend faces 250 of the laser-active regions 228 lie in one plane and endfaces 252 of the laser-inactive regions 232' in another plane, with thelatter plane being offset in the first direction 230 in relation to theone first mentioned.

Owing to the spacing of the two planes, the above-mentioned same phaseposition of the segments of the beams 20 and 22, respectively, passingthrough the laser-active regions 228 and the laser-inactive regions 232'can be achieved in the variant 214' of the laser-active unit.

In a further variant 214" of the laser-active unit, illustratedpartially in FIG. 16, the laser-inactive regions 232" are produced asmaterial-free channels 254 which extend parallel to the laser-activeregions 228" so that segment of the respective beam 20 and 22,respectively, run either through one of the laser inactive regions 228"with a pumped semiconductor layer or through one of the channels 254produced material by etching.

With this variant of the laser-active unit 214", too, the aim ispreferably for the phase position of the segments passing through thelaser-active regions 228" to be identical with that of the segments ofthe beams 20 and 22, respectively, passing through the laser-inactiveregions 232", i.e., through the channels 254 so that the expanse of thelaser-active regions 228" in the first direction 230 and the expanse ofthe channels 254 in the first direction 230 are likewise coordinated.

In all of the variants of the inventive laser-active unit, pumping ofthe laser-active regions 228, 228' and 228" is carried out in the usualway for semiconductor lasers with the pumping means 218 and isdescribed, for example, in Principles of Lasers, 3rd. Ed., by O. Svelto,Plenum Press, New York 1989 and/or in Handbook of Solid State Lasers, byP.K. Cheo, Marcel Dekker Inc., New York 1989.

For the rest, the fourth embodiment of the inventive solution operatesin the same way as the second embodiment and so reference is to be hadin full in this connection to the statements on the second embodiment.

In the same way as described by way of example in connection with thefourth embodiment in comparison with the second embodiment, replacementof the solid-state rods 46 and 48 by laser-active units 214, 214' and214" is also possible in the first and third embodiments.

In a fifth embodiment of the inventive solid-state laser, illustrated inFIG. 17, the optical resonator designated in its entirety 262 isrepresented as half of a confocal unstable resonator. Herein a convexmirror 264 and a concave mirror 266 are arranged facing one another andextend from an optical axis 268 of this resonator 262 in a transversedirection 270, the expanse of the convex mirror 264 in this transversedirection 270 being shorter than that of the concave mirror 266 so thata laser beam 272 starting from the concave mirror 266 emerges from theresonator 262 at the side of the convex mirror 264.

The confocal mirror surface 274 and 276, respectively, of the convexmirror 264 and the concave mirror 266 are preferably designed ascylindrical mirror surfaces and hence extend in a height direction 278perpendicular to the transverse direction 270 and perpendicular to theoptical axis 268 parallel to one another, as illustrated in FIG. 18.

Such as confocal resonator with cylindrical mirrors is described indetail, for example, in German patent 37 29 053 or in A.E. Siegman,Unstable Optical Resonators, Appl. Optics, 13, pages 353-367 (1974).

A plurality of excitation sections 280 is arranged between the mirrors264 and 266 in the beam path of the resonator 262. These excitationsections 280 lie between two coupling sections 282 and 284 immediatelyadjoining the mirrors 264 and 266, respectively. A joint beam of theresonator 262 is present in these coupling sections 282 and 284. Thisjoint beam 286 is coherent and has a beam path like that known inconfocal unstable resonators. The joint beam 286, for its part, is madeup of partial beams 292 lying directly alongside one another in thetransverse direction 270. For each excitation section 280, one of thepartial beams 292 of the joint beam 286 is imaged by means of an opticalelement 288 and 290, respectively, in the form of a cylindrical opticalmeans on either side of the excitation section 280 into a beam 294 inthis excitation section which extends with its longitudinal direction296 between the two cylindrical optical means 288 and 290. Thecylindrical optical means 288 and 290 image the partial beam 292 intothe beam 294 such that its extent in the transverse direction 25parallel to the transverse direction 270 is less than the extent of thepartial beam 292 in the transverse direction 270.

As illustrated in FIGS. 17 and 19, there is arranged in each excitationsection 280 a laser-active unit 214 whose laser amplification volume 216is penetrated by the beam 294 with an essentially parallel beam path,the first direction 230 of the laser amplification volume 216 extendingparallel to the direction of propagation 296 of the beam 294.Furthermore, the height 244 of the laser amplification volume 216extends parallel to the height direction 278. Hence the extent of thebeam 294 in the transverse direction 25 is less than or equal to theexpanse of the narrow side 236 of the laser-active regions 228.Furthermore, the width of the laser-active unit 214 in the transversedirection 270 corresponding at the most to the width of the respectivepartial beam 292 in this direction.

In the fifth embodiment, a plurality of laser-active units 214 areplaced close together and form a laser-active block 298, the laseramplification volume 216 of the individual laser-active units 214 beingarranged in succession at constant, equal spacings in the transversedirection 270.

The cylindrical optical means 288 and 290 are each designed such that,as mentioned previously, they image a partial beam 292 with anessentially parallel beam path and a certain extent in the transversedirection 270 into the beam 294 of the respective excitation section 280with an essentially parallel beam path, the extent of each partial beam292 in the transverse direction 270 being such that the followingpartial beam 292 immediately adjoining it is detected by the followingcylindrical optical means 288 and 290, respectively, and hence, in all,the joint beam 286 is imaged in the region of the laser-active block 298continuously into the beams 294 so that the block 298 appearstransparent for the joint beam 286 although there are non-transparentregions between the individual beams 294 of the individual excitationsections 280 but owing to the imaging by the cylindrical optical means288 and 290, these do not have a shading influence on the joint beam286.

Furthermore, in the design of the cylindrical optical means describedhereinabove, the beam divergence upon emergence of the beam 294 from thelaser amplification volume 216 owing to the small width of the beam 294in the transverse direction 25 has to be taken into consideration and sothe scattering effect of the cylindrical optical means 298 and 290 hasto be of correspondingly smaller dimensions.

The extent of the joint beam 286 in the height direction 278 is selectedsuch that it is at the most equal to or less than the extent of thelaser amplification volume 216 in the direction of the height 244.Moreover, the cylindrical optical means 288 and 290 are of suchdimensions that, for their part, they extend at least over the extent ofthe joint beam 286 in the height direction 278 and do, therefore, alsonot contribute to any switching-off of the joint beam in this direction.

The laser-active units 214 which form the laser block 298 can bedesigned in the same way as in the fourth embodiment or its variants sothat the block 298 can be made up of the laser-active units 214, 214'or214".

Therefore, regarding the design of the laser-active units 214, referenceis to be had in full to the statements on the fourth embodiment in thiscontext.

In a variant of the fifth embodiment, illustrated in FIG. 20, severallaser-active units 214a and 214b are arranged one behind the other ineach excitation section 280 in order to increase the amplification inthe individual excitation sections 280 by enlarging the extent of thelaser-active regions in the first direction 230. In this variant, in thesimplest case, the laser-active regions 228 are arranged in alignmentwith one another and the laser-inactive regions 232 in alignment withone another so that the optical lengths of the laser-active regions 228add up. This does, of course, require the dimensions of the laser-activeregions with respect to their narrow sides 236 and their broad sides 238as well as the dimensions of the laser-inactive regions 232 with respectto their narrow sides 240 and their broad sides 242 to be identical.

In a further variant, illustrated in FIG. 21, two laser-active units214c and 214d are likewise provided in each excitation section 280, thelaser-active unit 214d adjoining the layer-active unit 214c beingarranged such that its laser-active regions 228 are not in alignmentwith the laser-active regions 228 of the laser-active unit 214c butinstead with the laser-inactive regions 232 of the laser-active unit214d and, conversely, the laser-active regions 232 with the laser-activeregions 228 of the laser-active unit 214c.

In this case, it is particularly advantageous for the cross-sections ofthe regions in respective alignment with one another to be identical sothat, in all, each segment of each beam 294 passes one time through alaser-inactive regions 232 and another time through a laser-activeregion 228, and the laser-active regions 228 and the laser-inactiveregions 232 is both laser-active units 214d and 214c preferably haveequally long dimensions in the first direction 230 so that after passingthrough the two laser-active units 214c and 214d all of the segments ofthe beam 214 have the same phase position.

Common to both variants of the fifth embodiment is, however, always thatthe two laser amplification volumes 216 of the two laser-active units214a and b as well as 214c and d are in respective alignment with oneanother, have the same cross-section and the two layer amplificationvolumes 216 in alignment with one another are penetrated by a singlebeam 294.

In a sixth embodiment, illustrated in FIGS. 22 and 23, the resonator 300is designed as confocal, unstable resonator comprising spherical mirrors304 and 306 arranged symmetrically in relation to a resonator axis 302.The mirror 304 is a convex mirror and the mirror 306 a concave mirror,and the concave mirror 306 extends beyond the convex mirror 304 so thata ring-shaped laser beam 308 with rays running parallel to the resonatoraxis 302 emerges from the resonator 300 past the convex mirror 304.Hence the joint beam 286 extends symmetrically from the resonator axis302 as far as the emerging laser beam 308. Such resonators are describedin detail in A.E. Siegman, Unstable Optical Resonators, Appl. Optics,13, pages 353-367 (1974).

The extent of the joint beam in the transverse direction 270 is,therefore, identical with that in the height direction 278.

Two block 298e and 298f are provided in the sixth embodiment,illustrated in FIG. 22 and FIG. 23, and their laser amplificationvolumes 216a and 216b are respectively arranged in an excitation section280e and 280f and are penetrated by a beam 294e and 294f of therespective excitation section 280e and 280f. Each of the excitationsections 280e and 280f is provided on either side thereof with acylindrical optical means 288e, 290e and 288f, 290f, respectively, whichimage the beam 294e and 294f, respectively, in the respective excitationsection 280e and 280f, respectively, into the joint beam 286 so that thejoint beam 286 is, in turn, also present between the two excitationsections 280e and 280f. Moreover, in the sixth embodiment, the laserexcitation volumes 216e and 215f are arranged such that the laserexcitation volume 216e stands parallel to the height direction 278 butthe laser excitation volume 216f parallel to the transverse direction270. In the same way, the cylindrical optical means 288e, 290e and 288f,290f are arranged in tilted relation to one another through 90°respectively. Furthermore, the extent of both laser-active blocks 298eand 298f in the transverse direction 270 is preferably selected suchthat this identical.

Hence a homogenization of the laser amplification in the joint beam 286is achieved with the arrangement according to the sixth embodiment whereone time the width of the partial beam 292 parallel to the transversedirection 270 is reduced by imaging by the cylindrical optical means288e, 290e and another time the extent of parts of the partial beam 292in the height direction height 278 is compressed by the cylindricaloptical means 288f, 290f owing to the optical imaging by the cylindricaloptical means 288f, 290f.

In a seventh embodiment, illustrated in FIG. 24, the laser amplificationvolumes 216 of the block 298g and h are aligned parallel to one anotherbut are offset in relation to one another in the transverse direction270 such that each laser amplification volume 216h is seated between twolaser amplification volumes 216g. In the same way, the optical elements288g, 290g and 288h, 290h are also offset in relation to one another inthe transverse direction 270 so that, for example, part of the rays ofadjacent beams 294g is imaged into the beam 294h by each optical element288h.

In the fifth, sixth and seventh embodiments, it is likewise possible forthe laser-active units 214, 214' and 214" to be replaced by thesolid-state rods 46 and 48, with optical pumping occurring in thedirection of the height direction 278, for example, in the fifth andseventh embodiments.

I claim;
 1. Solid-state laser comprising a laser-active unit with alaser amplification volume (46, 48, 216) extending in a first directionin a solid, a pump means (174, 192, 218) associated with said laseramplification volume (46, 48, 216) for exciting said laser amplificationvolume and a resonator (152, 262, 300) with an excitation section (14,16, 280) arranged between its resonator mirrors and a beam (20, 22, 294)extending in a direction of propagation (21, 23 296) in said excitationsection and thereby penetrating said laser amplification volume (46, 48,216) in said first direction (50, 52, 230), characterized in that atleast two excitation sections (14, 16, 218) are provided, each havingone laser amplification volume (46, 48, 216), in that said beams (20,22, 294) of said excitation sections (14, 16, 280) extend in spacedrelation to one another, in that said resonator (152, 262) has acoupling section (28, 282, 284) containing a coherent joint beam (121,286) of said resonator (152, 262), the cross-section thereof beingcomprised of several partial beams (24, 26, 292), and in that an opticalelement (156, 288, 290) is arranged between said coupling section (28,282, 284) and each excitation section (14, 16, 280) for imaging one ofsaid partial beams (24, 26, 292) of said joint beam (121, 286) into oneof said beams (20, 22, 294) extending in spaced relation to one anotherin said excitation sections (14, 16, 280).
 2. Solid-state laser asdefined in claim 1, characterized in that said partial beams (24, 26,292) form a joint beam (121, 286) which is coherent in thecross-sectional direction.
 3. Solid-state laser as defined in claim 1,characterized in that said optical element (156, 288, 290) images therespective partial beam (24, 26, 292) into said beam (20, 22, 294) suchthat the latter is narrowed in a cross-sectional direction (162, 270) inrelation to said partial beam (24, 26, 292).
 4. Solid-state laser asdefined in claim 3, characterized in that said laser-active unit has insaid cross-sectional direction a width which corresponds at the most toa width of said partial beam imaged by said optical element onto saidbeam in said cross-sectional direction.
 5. Solid-state laser as definedin claim 4, characterized in that said optical elements (156, 288, 290)of excitation sections (14, 16, 280) lying alongside one another adjoinone another and image partial beams (24, 26, 292) of said joint beam(121, 286) immediately adjoining one another essentially continuouslyinto said beams (20, 22, 294) lying alongside one another and in spacedrelation to one another.
 6. Solid-state laser as defined in claim 4,characterized in that said laser-active unit has supply elementsarranged in said cross-sectional direction beside said amplificationvolume for the latter.
 7. Solid-state laser as defined in claim 1,characterized in that said optical element comprises a cylindricaloptical means for each beam.
 8. Solid-state laser as defined in claim 1,characterized in that said optical element images parallel rays of saidjoint beam into quasi-parallel ray of said beam.
 9. Solid-state laser asdefined in claim 1, characterized in that said laser amplificationvolumes are spaced from one another.
 10. Solid-state laser as defined inclaim 9, characterized in that said laser amplification volumes (46, 48,216) are arranged at regular spacings from one another.
 11. Solid-statelaser as defined in claim 1, characterized in that said beamspenetrating different laser amplification volumes run parallel to oneanother.
 12. Solid-state laser as defined in claim 1, characterized inthat each layer amplification volume is cooled on at least one sideextending parallel to said beam.
 13. Solid-state laser as defined inclaim 12, characterized in that said cooled side is the side (60, 62,238) facing said adjacent laser amplification volume (46, 48, 216). 14.Solid-state laser as defined in claim 1, characterized in that eachlaser amplification volume is excitable from at least one excitationside extending parallel to said beam.
 15. Solid-state laser as definedin claim 1, characterized in that said laser amplification volume isformed by an optically excitable solid-state rod.
 16. Solid-state laseras defined in claim 15, characterized in that said pumping means (70,72, 174, 192) irradiates said solid-state rod from one side. 17.Solid-state laser as defined in claim 16, characterized in that thepumping power impinges on one narrow side of said solid-state rod. 18.Solid-state laser as defined in claim 15, characterized in that at leastone broad side of said solid-state rod is cooled.
 19. Solid-state laseras defined in claim 15, characterized in that said solid-state rod hasan essentially four-cornered cross-section with two broad sidesextending essentially perpendicular to two narrow sides thereof. 20.Solid-state laser as defined in claim 15, characterized in that saidsolid-state rod is coolable by contact with a flow-free material. 21.Solid-state laser as defined in claim 20, characterized in that saidsolid-state rod is cooled by contact with a cooling element. 22.Solid-state laser as defined in claim 21, characterized in that saidcooling element is surrounded by said pumping power source. 23.Solid-state laser as defined in claim 21, characterized in that saidcooling element (68, 146, 166) rests against said solid-state rod (46,48) with a press fit.
 24. Solid-state laser as defined in claim 21,characterized in that said cooling element carries said solid-state rod.25. Solid-state laser as defined in claim 21, characterized in that saidlaser amplification volume is seated with two broad sides and a narrowside in a groove of said cooling element.
 26. Solid-state laser asdefined in claim 15, characterized in that said solid-state rod iscoolable on sides thereof facing one another.
 27. Solid-state laser asdefined in claim 15, characterized in that a plurality of solid-staterods are adapted to be acted upon with pumping power on their sides thatface away from one another.
 28. Solid-state laser as defined in claim15, characterized in that elements are provided for concentrating thepumping power onto said solid-state rods.
 29. Solid-state laser asdefined in claim 28, characterized in that said elements (78, 80) forconcentrating said pumping power deflect onto said solid-state rods (46,48) electromagnetic radiation which has been emitted by said pumpingpower source (70, 72, 174, 192) into a solid angle.
 30. Solid-statelaser as defined in claim 28, characterized in that said elements forconcentrating said pumping power are reflectors.
 31. Solid-state laseras defined in claim 28, characterized in that intermediate webs of saidcooling element are designed as said elements concentrating said pumpingpower onto said solid-state rods.
 32. Solid-state laser as defined inclaim 15, characterized in that said pumping power means comprise agas-discharge lamp.
 33. Solid-state laser as defined in claim 32,characterized in that a gas discharge is generated in said gas-dischargelamp (174) by a field extending essentially radially in relation to theaxis thereof.
 34. Solid-state laser as defined in clam 32, characterizedin that a gas discharge is generated in said gas-discharge lamp (174) bya field extending azimuthally in relation to the axis thereof. 35.Solid-state laser as defined in claim 32, characterized in that gasdischarge can be generated in said gas-discharge lamp withhigh-frequency.
 36. Solid-state laser as defined in claim 15,characterized in that said pumping power means are comprised of singlepumping power sources.
 37. Solid-state laser as defined in claim 15,characterized in that said pumping power means comprise semiconductordiodes.
 38. Solid-state laser as defined in claim 1, characterized inthat said laser amplification volume is that of a laser-active unit of asemiconductor laser assembly.
 39. Solid-state laser as defined in claim38, characterized in that several laser-active regions (228) areprovided in each laser amplification volume (216).
 40. Solid-state laseras defined in claim 39, characterized in that said laser-active regions(228) are arranged in spaced relation to one another.
 41. Solid-statelaser as defined in claim 40, characterized in that laser-inactiveregions (232) are arranged in spaced between laser-active regions (228).42. Solid-state laser as defined in claim 41, characterized in that saidlaser-inactive regions (232) are of transparent design for said beam(20, 220, 294).
 43. Solid-state laser as defined in claim 42,characterized in that said laser-inactive regions (232) are in the formof semiconductor layer regions but with an increase band gap in relationto said laser-active regions.
 44. Solid-state laser as defined in claim42, characterized in that said laser-inactive regions (232) are in theform of material-free channels (254).
 45. Solid-state laser as definedin claim 42, characterized in that the optical length of saidlaser-active and said laser-inactive regions is of such dimensions thatthe parts of said beam penetrating these differ in phase by an integralmultiple of
 2. 46. Solid-state laser as defined in claim 1,characterized in that the same partial beam, imaged as one of said beamsextending in a direction of propagation in said excitation section,penetrates two laser amplification volumes of two laser-active units,said laser amplification volumes being arranged in succession in thedirection of propagation of said one said beam.
 47. Solid-state laser asdefined in claim 46, characterized in that said laser-active units (214)are arranged either immediately one behind the other or in the form oftwo excitation sections (280) between which imaging into a partial beamagain takes place.
 48. Solid-state laser as defined in claim 46,characterized in that said laser-active regions are in alignment withone another.
 49. Solid-state laser as defined in claim 46, characterizedin that said laser-active regions of different laser-active units arearranged in off-set relation to one another.
 50. Solid-state laser asdefined in claim 46, characterized in that said laser-active units arearranged in turned relation to one another about an axis parallel tosaid direction of propagation.
 51. Solid-state laser as defined in claim46, characterized in that several laser-active units are arrangedalongside one another in sandwich-like configuration.
 52. Solid-statelaser as defined in claim 51, characterized in that said laseramplification volume is formed by an optically excitable solid-staterod.
 53. Solid-state laser as defined in claim 51, characterized in thatsaid laser amplification volume is that of a laser-active unit ofsemiconductor laser assembly.
 54. Solid-state laser comprising aresonator, at least one laser amplification volume arranged in saidresonator and a pumping means for exciting said laser amplificationvolume, characterized in that said resonator (12, 112, 152) is a coupledresonator, in that said resonator (12, 112, 152) has two elongatedexcitation sections (14, 16), one of said laser amplification volumes(46, 48, 216) being arranged in their beam (20, 22), respectively, inthat said resonator (12, 112, 152) has a coupling section (28) which thebeams of said excitation sections (14, 16) enter as outer beams (24, 26)extending in spaced relation to one another and which couples saidexcitation sections (14, 16) with one another by displacing said outerbeams (24, 26) in the plane defined by these to a coupling axis (30)lying between these and beyond this coupling axis (30), and in that saidlaser amplification volumes (46, 48, 216) are cooled on a side (60, 62,66) extending along said beam and are excitable by said pumping means(70, 72, 174, 192, 218) from a side (64, 238) extending along said beam.55. Solid-state laser as defined in claim 54, characterized in that saidcoupling section (28) comprises the beam path of an unstable resonator.56. Solid-state laser as defined in claim 54, characterized in that saidouter beams lie symmetrically in relation to said coupling axis. 57.Solid-state laser as defined in claim 54, characterized in that saidcoupling section comprises a mirror which reflects towards said couplingaxis and a mirror which reflects away from said coupling axis. 58.Solid-state laser as defined in claim 57, characterized in that saidcoupling axis is an axis of symmetry of said mirrors of said couplingsection.
 59. Solid-state laser as defined in claim 57, characterized inthat said mirrors of said coupling section have cylindrical mirrorsurfaces.
 60. Solid-state laser as defined in claim 57, characterized inthat said mirrors of said coupling section are shaped so as to havespherical mirror surface and extend symmetrically with respect torotation around said coupling axis.
 61. Solid-state laser as defined inclaim 57, characterized in that both of said mirrors (38, 40) displacesaid outer beams (24, 26) in the direction toward said coupling axis(30) and image these in reduced size towards it.
 62. Solid-state laseras defined in claim 57, characterized in that said mirror reflectingtowards said coupling axis protrudes with its active region in theradial direction in relation to said coupling axis beyond the activeregion of said mirror reflecting away from said coupling axis and isacted upon by said outer beams in this protruding region. 63.Solid-state laser as defined in claim 54, characterized in that saidexcitation sections are closed off by end mirrors on each side facingaway from said coupling section.
 64. Solid-state laser as defined inclaim 63, characterized in that said end mirrors (32, 34, 168) reflectsaid beams (20, 22) in said excitation sections (14, 16) into saidcoupling section (28).
 65. Solid-state laser as defined in claim 63,characterized in that said end mirrors comprise a curvature whichcompensates expansion of said beam in said excitation section andreflects the radiation coming from said coupling section back intoitself.
 66. Solid-state laser as defined in claim 65, characterized inthat said end mirrors closing off said excitation sections are joinedtogether to form a mirror ring.
 67. Solid-state laser as defined inclaim 54, characterized in that several outer beams are provided andthese are respectively arranged in different planes extending throughsaid coupling axis and continue respectively in corresponding excitationsections.
 68. Solid-state laser as defined in claim 67, characterized inthat said outer beams form annular segments in relation to said couplingaxis.
 69. Solid-state laser as defined in claim 68, characterized inthat said coupling section is closed off in those annular segments inwhich there are no incident outer beams from said excitation sections bymirrors which reflect back.
 70. Solid-state laser as defined in claim67, characterized in that the sum of all outer beams essentially forms aclosed annulus in said coupling section.
 71. Solid-state laser asdefined in claim 54, characterized in that an optical element isprovided between said coupling section and said excitation sections forimaging said outer beams onto said beams in said excitation sections.72. Solid-state laser as defined in claim 71, characterized in that saidoptical element comprises a cylindrical optical means (156). 73.Solid-state laser as defined in claim 72, characterized in that saidcylindrical optical means comprises a cylindrical, optical annularsegment (156) which images said outer beam (24, 26) forming an annularsegment in said coupling section (28) onto a beam (20, 22) narrower insaid azimuthal direction (162) in relation to said coupling axis (30) insaid excitation section (14, 16).
 74. Solid-state laser as defined inclaim 73, characterized in that the cylindrical, optical annularsegments (156) supplement one another to form an annulus (154).